In recent years, in consideration of demand of society, such as environmental protection and nature conservation, researches have been actively conducted on a fuel cell, which is an energy source which is high in efficiency and low in environmental load. Among various types of fuel cells, a polymer electrolyte fuel cell (PEFC) has drawn people's attention as an energy source for home use or an energy source for vehicles because it is advantageous in that its operation temperature is low and its output density is high. Such a polymer electrolyte fuel cell uses, as a fuel, hydrogen which is more likely to leak as compared with other fuels. Therefore, it is considered that a gas detector which detects leakage of hydrogen becomes necessary for practical implementation of the polymer electrolyte fuel cell.
Also, researches have been actively conducted on a hydrogen internal combustion engine which is an energy source which is low in environmental load and which uses hydrogen as a fuel like the polymer electrolyte fuel cell. As to the hydrogen internal combustion engine as well, it is considered that a gas detector which detects leakage of hydrogen becomes necessary for practical implementation.
A gas detector including a heat generation resistor has been known as a gas detector for detecting leakage of a specific gas (e.g., hydrogen) in a to-be-detected atmosphere. This gas detector measures the quantity of heat taken from the heat generation resistor by the to-be-detected atmosphere and calculates a change in the thermal conductivity of the to-be-detected atmosphere to thereby obtain the concentration of the specific gas (hydrogen concentration).
There has been known a gas detector which has a Wheatstone bridge circuit including a heat generation resistor as one of four resistor sections thereof and which measures the quantity of heat taken from the heat generation resistor by the to-be-detected atmosphere through use of the Wheatstone bridge circuit (see, for example, Patent Document 1).